My friend is storing an air compressor with me, so air-powered tools are an option. I'd need to buy fittings and an air hose, though.

I do own red (left) aviation snips, but for this much cutting, I think I'd buy yellow (straight) snips for ease of use.

The manufacturer gives this guidance:

Steel roofing and trim should be cut with nibblers, tin snips or a
profile shear. Although Champion Metal of WA. does not advocate the
use of a saw, the reality is many people use a power saw in some
manner. There are two concerns when using a saw. First, be sure that
no burrs are left on the ends of the panel. The rough edges are not
protected and will rust. Second, the filings coming off the blade are
hot and will adhere to the surface of the panels and these will rust.
Be sure all filings are removed from the surface as they will rust and
pit the surface of the sheet.

Should I just use hand-snips? Buy an drill attachment? A metal blade in a circular saw? Buy an electric- or air-powered tool? Try to rent something? Maybe the roofing dealer will loan a cutting tool?

5 Answers
5

I used to use a 7 1/4" metal cutting wheel on a circular saw. Works good, but wheel wears down fairly fast. There are also some good shear attachments that mount on drills. I'd advise you to make the cuts on the end going to the top, not the exposed bottom. Definitely have some spray paint or primer to treat the cut end, because it will rust. If you put the cut ends at the top under your ridge cap, you will be fine. The other alternative is to buy your panels cut to length before they land on the job. Several manufactures cut to order such as Everlast Metal Roofing.

Jay, I have installed over 100 metal roofs, so got a few more tips for ya. Install your strapping, starting at the bottom, 2 feet OC with an extra on top if needed. Put your drip edges on first. Stack four to six panels on top of eachother, properly orientated for anti siphon edges and top of panel. Snap a chalk line across the top panel to align to centers of your strapping and predrill the whole stack with 1/8" bit to get perfect placement and easy starts. Square the first panel on the roof to your drip line and put a few screws in. Place panels and secure. go back and finish screws.
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shirlock homesSep 30 '12 at 11:40

You can make a good cutting blade for sheet metal roofing out of a cheap circular saw blade.

Go find your old used circular wood cutting blades, without carbide teeth, or buy the cheapest circular saw blade you can buy. There is no point in messing
up a good carbide tooth blade. They can be easily re-sharpened.

Circular saw blades usually cut about 1/8 inch wide.
If you look at them, you will see the teeth are angled outward to make the 1/8 inch cut. But the
blade itself is approximately 1/16 inch wide.

So take the used or new blade and stick
it in a vise. Use an angle (side) grinder to make
all the teeth no wider than the rest of the blade.
This is easy to do. If you do not have an angle
grinder (like one a welder uses) then put the cheap
blade in the circular saw and turn it against a
grinding stone or grinding wheel. When you are done the teeth are 1/16 wide.

All the grinding will be on the
sides of the teeth. Do not grind the teeth off of the blade , only the sides of the teeth. When you finish, the blade's teeth will be thinner, but the ends of the teeth are not shorter. This should take
only a couple of minutes. Do not make the blade any
thinner except at the teeth. This blade has no need of sharpening. It dulls up as soon as it hits the
metal - and cuts fine.

Now you can mount the blade in the saw and cut the roofing metal, but you are only removing
1/16 of an inch, a much thinner and easier cut.

Metal roofing with ribs cuts easier from the back side(the down side when screwed to the roof). I use pencil lines, pop lines are too fuzzy.

You can run this thin blade forwards or backwards,
but after it makes a few cuts, the teeth are not
sharp and direction makes little difference.

This blade will last FOREVER. It will not need ANY
sharpening.

YOU, however, WILL need earplugs. The easiest place
to cut metal roofing is on the grass. The metal
sheets slide around too much on a bench or table.
Lay a 2x4 on the grass and hang the end of the metal panel over the 2x4. Now your blade is not digging into the turf as you cut.

I have cut painted and unpainted Galvalume metal roofing this way. If you get hung up or the blade
is pinched by the metal, stop and adjust. The blade
needs to keep moving so it does not get hot and
mess up the paint on painted galvalume.

P.S.
You can get clean edges by running a 4 inch angle
grinding wheel along the edge where you cut. This
should be done RAPIDLY, to just remove the burrs.
If you stop moving, the grinder will dig in where
you don't want it to. Don't push hard on the wheel
- just lightly remove the burrs left over from cutting. This makes a nice smooth edge if your cut
was straight.

I have found very little rust on these smoother cut
edges and I live in a wet climate. I think the zinc in the galvalume migrates to the edge somehow.

The roofers I've seen working with metal sheet cladding have usually used an air or electric nibbler to cutting single sheets. Composite sheets (metal, insulation, metal sandwich) generally get cut with a carbide tipped circular saw.

In addition to a nibbler, I've also used a grinder to cut metal sheet, but as mentioned, it does usually leave a bit of a messy burr on the cut edge.

1 - I would recommend first electric shears. They are fast and will give you a clean cut with no burned edges. See here. This is not the exact model I use, but it's pretty close. Navigate to the electric shear page for more options. This are fast and very reliable.

2 - Regular long snips. The 12" Andy snips from this page are one of the best you can find. Considering its 29 gauge, you should be able to cut through like paper.